1. Technical Field
This invention relates to photo-stimulable storage phosphor apparatus and more particularly to a storage phosphor reader having apparatus for correctly transferring a storage phosphor plate between a cassette and the reader.
2. Background Art
In a photo-stimulable storage phosphor imaging system, as described in U.S. Pat. No. Re. 31,847 reissued Mar. 12, 1985 to George W. Luckey, a photo-stimulable phosphor sheet is exposed to an imagewise pattern of short wavelength radiation, such as X-radiation, to record a latent image pattern in the photo-stimulable phosphor sheet. The latent image is read out by stimulating the phosphor with a relatively long wavelength stimulating radiation, such as red or infrared light. Upon stimulation, the photo-stimulable phosphor releases emitted radiation of an intermediate wavelength, such as blue or violet light, in proportion to the quantity of short wavelength radiation that was received. To produce a signal useful in electronic image processing, the photo-stimulable phosphor sheet is scanned in a raster pattern by a beam of light produced, for example, by a laser deflected by an oscillating or rotating scanning mirror, and the emitted radiation is sensed by a photodetector such as photomultiplier tube to produce the electronic image signal.
In applications in which the photo-stimulable storage phosphor sheet is exposed to X-radiation at one location and read out at another location, it is desirable that the photo-stimulable storage phosphor sheet not be exposed to undesirable light to prevent image degradation. It is also desirable that the storage phosphor sheet be protected from damage during handling between the exposure and read out stations. It has thus been proposed to support a storage phosphor in a rigid cassette to shield the storage phosphor from extraneous light and to protect it from damage. To assure that a storage phosphor is transferred properly into a reader for scanning the phosphor, it is desirable that the cassette be properly oriented relative to the reader. Moreover, where different size cassettes are used, it is desirable that each cassette be oriented in the same manner.